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block: properly protect the 'queue' kobj in blk_unregister_queue

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The original commit e9a823fb34 (block: fix warning when I/O elevator
is changed as request_queue is being removed) is pretty conflated.
"conflated" because the resource being protected by q->sysfs_lock isn't
the queue_flags (it is the 'queue' kobj).

q->sysfs_lock serializes __elevator_change() (via elv_iosched_store)
from racing with blk_unregister_queue():
1) By holding q->sysfs_lock first, __elevator_change() can complete
before a racing blk_unregister_queue().
2) Conversely, __elevator_change() is testing for QUEUE_FLAG_REGISTERED
in case elv_iosched_store() loses the race with blk_unregister_queue(),
it needs a way to know the 'queue' kobj isn't there.

Expand the scope of blk_unregister_queue()'s q->sysfs_lock use so it is
held until after the 'queue' kobj is removed.

To do so blk_mq_unregister_dev() must not also take q->sysfs_lock.  So
rename __blk_mq_unregister_dev() to blk_mq_unregister_dev().

Also, blk_unregister_queue() should use q->queue_lock to protect against
any concurrent writes to q->queue_flags -- even though chances are the
queue is being cleaned up so no concurrent writes are likely.

Fixes: e9a823fb34 ("block: fix warning when I/O elevator is changed as request_queue is being removed")
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Mike Snitzer 2018-01-11 14:11:01 -05:00 committed by Jens Axboe
parent bc8d062c36
commit 667257e8b2
2 changed files with 11 additions and 11 deletions
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9
block/blk-mq-sysfs.c
View File

@ -248,7 +248,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
return ret;
}
static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
int i;
@ -265,13 +265,6 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
q->mq_sysfs_init_done = false;
}
void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
{
mutex_lock(&q->sysfs_lock);
__blk_mq_unregister_dev(dev, q);
mutex_unlock(&q->sysfs_lock);
}
void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx)
{
kobject_init(&hctx->kobj, &blk_mq_hw_ktype);

13
block/blk-sysfs.c
View File

@ -929,13 +929,18 @@ void blk_unregister_queue(struct gendisk *disk)
if (WARN_ON(!q))
return;
/*
* Protect against the 'queue' kobj being accessed
* while/after it is removed.
*/
mutex_lock(&q->sysfs_lock);
queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
mutex_unlock(&q->sysfs_lock);
spin_lock_irq(q->queue_lock);
queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
spin_unlock_irq(q->queue_lock);
wbt_exit(q);
if (q->mq_ops)
blk_mq_unregister_dev(disk_to_dev(disk), q);
@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk)
kobject_del(&q->kobj);
blk_trace_remove_sysfs(disk_to_dev(disk));
kobject_put(&disk_to_dev(disk)->kobj);
mutex_unlock(&q->sysfs_lock);
}